Wellbore telemetry apparatus

ABSTRACT

An apparatus having coiled conductor stored therein is used in a wellbore telemetry system. The telemetry system permits the monitoring of a subsurface condition as drilling proceeds. The apparatus includes a tubular container, an insulated electric conductor mounted in the container in a configuration which includes left-hand and right-hand coils, and means for dispensing conductor from opposite ends of the container. The apparatus permits the conductor string to be lengthened as the drill string is lengthened.

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Kostelnicek ate [191 [4 1 Sept. 9, 1975 WELLBORE TELEIVIETRY APPARATUSRichard J. Kostelnicek, Houston, Tex.

[75] Inventor:

[73] Assignee: Exxon Production Research Company, Houston, Tex.

[22] Filed: May 31, 1974 [21] Appl. N0.: 475,010

521 US. Cl. 191/12 R; 174/69 51 Int. (:1. ..1-102(; 11/00 [58] Field ofSearch 174/69, 47, 35, 135;

[56] References Cited UNITED STATES PATENTS 3,285,629 11/1966 Cullen175/104 3,608,125 9/1971 Nelson 191/12 R 7/1973 Bernard .1 174/69 5/1974Fletcher 174/69 Primary Examiner--M. Henson Wood, Jr. AssistantExaminerD. W. Keen Attorney, Agent, or Firm-Robert L. Graham 5 7]ABSTRACT An apparatus having coiled conductor stored therein is used ina wellbore telemetry system. The telemetry system permits the monitoringof a subsurface condition as drilling proceeds. The apparatus includes atubular container, an insulated electric conductor mounted in thecontainer in a configuration which in-' cludes left-hand and right-handcoils, and means for dispensing conductor from opposite ends of thecontainer. The apparatus permits the conductor string to be lengthenedas the drill string is lengthened.

8 Claims, 8 Drawing Figures PATENTEUSEF 197s SHEET 1 [IF 3 WELLBORETELEMETRY APPARATUS BACKGROUND OF THE INVENTION l. Field of theInvention This invention relates to an improved apparatus for use inwell-bore telemetry operations. In one aspect, it relates to an improvedcable system for maintaining electric continuity between surface andsubsurface locations in a drill string.

2. Description of the Prior Art In the drilling of oil wells, gas wells,and similar boreholes, it frequently is desirable to transmit electricenergy between subsurface and surface locations. One application whereelectrical transmission has received considerable attention in recentyears is found in wellbore telemetry systems designed to sense,transmit, and receive information indicative of a subsurface condition.This operation has become known in the art as logging while drilling." Amajor problem associated with wellbore telemetry systems proposed in thepast has been that of providing reliable means for transmitting anelectric signal between the subsurface and surface locations. Thisproblem can best be appreciated by considering the manner in whichrotary drilling operations are normally performed. In rotary drilling, aborehole is advanced by rotating a drill string provided with a bit.Sections of drill pipe, approximately 30 feet in length, are addedindividually to the drill string as the borehole is advanced. Inadapting an electrical telemetry system to rotary drilling equipment, itwill thus be appreciated that the means for transmitting an electricsignal between subsurface and surface locations must be such as topermit the addition of individual pipe sections to the drill string. Anearly approach to the problem involved the use of a continuouselectrical cable which was adapted to be lowered inside the drill stringand to make contact with a subsurface instrument. This technique,however,'required withdrawing the cable each time a pipe section wasadded to the drill string. A more recent approach involves the use ofspecial drill pipe equipped with an electric conductor. Each pipesection is provided with connectors that mate with connectors of anadjacent pipe section and thereby provide an electrical circuit acrossthe joint (U.S. Nos. 3,518,608 and 3,518,609). Disadvantages of thissystem include the need for special pipe sections and the difficulty ofmaintaining insulation of the electrical connectors at the pipe sectionjoints.

SUMMARY OF THE INVENTION The apparatus of the present invention isadapted for use in well drilling operations wherein an electricconductor disposed in a pipe string is employed to transmit electricenergy between a subsurface and surface loca-v tion.

A novel feature of the invention involves the configuration of aconductor within a drill string which permits storage of excessconductor. The invention contemplates the use ofa tubular container formaintaining the electric conductor within the drill string in a coiledconfiguration and for uncoiling the conductor as additional conductor isneeded. Thus, as the drill string is lengthened, the electric circuitbetween the subsurface and surface can be maintained merely bydispensing the coiled portions of the conductor until the excessconductor stored in the container is used up. The coiled conductor ismaintained in the container in coiled portions wound in opposite hands,i.e. one portion is provided with left-hand coils and a second withright-hand coils. Means are provided for paying out the conductor fromthe top and bottom of the container in such a manner that the individualleft-hand and righthand coils are unwound at about the same time oralternatively, thereby preventing twists from forming in the conductorstring.

In a preferred embodiment of the invention, the apparatus comprises anelongated open-ended tube capable of being lowered into a pipe stringused to drill a well, an electric conductor or cable mounted in the tubehaving a first portion wound in left-hand coils and a second portionwound in right-hand coils, and means for dispensing the coiled portionsfrom opposite ends of the tube. A preferred form of the dispensing meansincludes cable brake or clutch which in response to the tension in theconductor string operates to reduce gripping force on the conductor. Inone embodiment a cable clutch is provided at each end of the tube forseparately gripping cable dispensed from the lefthand coils and from theright-hand coils. One clutch operates in response to movement of theother clutch to enable dispensing of cable from opposite ends at aboutthe same rate. This may be achieved by unwinding the coils at about thesame rate or unwinding left-hand and right-hand coils alternatively.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1. isa schematic view of welldrilling equipment provided with a telemetry system for monitoring asubsurface condition FIG. 2 is an enlarged longitudinal sectional viewof a container employed in the telemetry system shown in FIG. 1illustrating the coiled configuration of the con ductor stored in thecontainer.

FIG. 3 is a cross-sectional view of the drill pipe shown in FIG. 1, thecutting plane taken along the line 3-3 thereof.

FIG. 4 is a cross-sectional view of the apparatus shown in FIG. 2, withthe cutting plane taken along the line 44 thereof.

FIG. 5 is a cross-sectional view of the apparatus shown in FIG. 2, thecutting plane taken along line 5-5 thereof.

FIGS. 6, 7, and 8 are schematic views, illustrating sequential steps foradding a section of drill pipe to the drill string.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventional rotary drillingequipment, as schematically illustrated in FIG. 1, includes swivel l0,kelly ll, tubular drill string 12, and bit 13. These components,connected in the manner illustrated, are suspended from the drillingderrick 14 by means of rig hoisting equipment. The kelly 11 passesthrough rotary table 16 and connects to the upper end of the drillstring 12. The term drill string as used herein refers to the column oftubular pipe 12 between the bit 13 and the kelly I l; and the term pipestring refers to the complete pipe column including kelly 11. The majorportion of the drill string normally is composed of drill pipe with alower portion being composed of drill collars. The drill string 12consists of individual pipe sections connected together in end-ro-endrelation by threaded connections. One connection is illustrated at 15 inFIG. I. In

the lower four sections of FIG. 1, the diameters of the borehole and thedrill string 12 have been expanded in relation to the upper section toreveal further details.

The borehole 17 is advanced by rotating the drill string 12 and bit 13while at the same time drilling fluid is pumped through the drill string12 and up the borehole annulus. The drilling fluid is delivered toswivel through a hose attached to connection 18 and is returned to thesurface fluid system through pipe 19. A kelly bushing 20 couples therotary table 16 to the kelly 11 and provides means for transmittingpower from the rotary table 16 to the drill string 12 and bit 13. (Theuse of a power swivel eliminates the need for the kelly and rotarytable. The present invention may be used with either system; forpurposes of illustration, however, it will be described in connectionwith the kelly and r0- tary table system.)

As mentioned previously, it frequently is desirable to monitor asubsurface drilling condition during drilling operations. This requiresmeasuring a physical condition at the subsurface location, transmittingthis data as an electrical signal to the surface, and reducing thesignal to useful form. Typical situations where telemetry is applicablein drilling operations include drilling through abnormal pressure zones,drilling through zones where hole deviation is likely to be a problem,directional drilling, exploratory drilling, and the like.

Although the present invention may be employed in most any drillingoperation wherein an electric conductor is used in tubular pipe totransmit electric energy between subsurface and surface locations, itfinds particularly advantageous application in a wellbore telemetrysystem such as that illustrated in FIG. 1 comprising an instrument 21,electric conductor 22, and receiver 23.

The instrument 21 capable of measuring a subsurface condition andgenerating an electric signal indicative of that condition is providedwithin the drill string 12. A variety of devices capable of sensing aphysical condition are available. These include transducers formeasuring pressure, temperature, strain and the like; surveyinginstruments for measuring hole deviation; and logging instruments formeasuring resistivity or other properties of subsurface formations. Theinstrument 21 may be powered by batteries or by energy transmittedthrough conductor 22. Alternatively, a subsurface generator driven byfluid flowing through the drill string 12 may be used to powerinstrument 21.

The present invention is concerned primarily with the apparatus forstoring portions of the electric conductor 22 is a coiled configurationwithin the drill string 12. The energy transmitted through the conductor22 may be a signal generated by the subsurface instrument 21 andtransmitted to the receiver 23 at the surface. Alternatively, the energymay be electric power transmitted from the surface to actuate or drive asubsurface instrument or motor, Or, energy may be transmitted down theconductor 22 to power the instrument 21 and simultaneously intelligencemay be transmitted up the same conductor.

As applied in telemetry operations, it is preferred that the energybeing transmitted be in the form of a pulsating signal. Information canbe transmitted by varying the number, amplitude, width or spacing of atrain of amplitude of the pulsating signal. More than one transducer orother device may be employed in the instrument 21 if desired, in whichcase a multiplexer may be used for sending the various signals over asingle pair of conductors.

The instrument 21 may be mounted directly in the drill string 12 or, asillustrated in FIG. 1, it may be a separate tool that is lowered intothe drill string 12 on the conductor 22.

The conductor 22 extends from the subsurface instrument 21 substantiallythrough the drill string 12, and connects to a suitable conductor 24,provided in the kelly l 1 (see FIG. 8). Conductor 24 may be embedded inthe kelly 11, in which case the conductor 22 will extend to the upperend of the drill string 12 and connect to conductor 24 at that point. Inorder to facilitate the addition of pipe sections to the drill string12, however, it is preferred that conductor 24 be disposed within kelly1 1 and extend slightly more than the length of one pipe section belowkelly 11. If telemetry operations are to be performed while the kelly 11and drill string 12 are rotating, the upper end of conductor 24 will beconnected to a device 25 capable of transmitting electric energy from arotating member to a stationary member. Device 25 may be a rotarytransformer having a rotor secured to the kelly 11 and a stator securedto the stationary portion of the swivel 10, or it may be a slip ring andbrush assembly. Electric conductor 29 interconnects the stationaryportion of device 25 and receiver 23 and conductor 39 may be grounded tothe pipe string providing a return path for the circuit. If telemetryoperations are to be performed at times when the drill string 12 andkelly 11 are stationary, the conductors 29 and 39 may be connecteddirectly to conductor 24 and the pipe string through a suitableconnector. In this situation, conductors will be disconnected when thekelly 11 and drill string 12 are rotated. Other means for transmittingthe signal to the receiver 23 include a wireless transmitter connectedto conductor 22 and located on a rotating member, e.'g. kelly 11.

The receiver 23 is an instrument capable of receiving the signalgenerated by instrument 21 and reducing it to useful form.

In accordance with the present invention, the conductor 22 is arrangedwithin the drill string 12 in a configuration such that the total lengthof the conductor 22 is substantially longer than the distance betweenthe subsurface instrument 21 and the surface. As described in detailbelow, the excess length of conductor 22 stored in the drill string 12permits the conductor 22 to be extended as the drill string 12 islengthened.

In one aspect,. the present invention contemplates storing the excesscable in the form of coils within the drill string 12 in canisters ortubular containers shown generally as 26 in FIG. 1. The containers 26may be constructed of metal or plastic and have a diameter sufficientlysmall to permit them to pass internally of the drill string 12. In thepreferred form of the invention, several of the containers 26 will beused in the conductor string 22 and each will provide sufficient lengthof excess cable stored therein to permit the addition of severalsections of drill pipe before another container with stored conductorwill be required. By coiling the conductor within the tube, substantiallengths of excess cable can be stored therein. For standard A.P.I. drillpipe having an inside diameter of 2.64 inches, a 2.5

inch O.D. container is capable of storing 50 feet of Va inch unarmoredcable per foot of container. A 10ft. l container thus is capable ofstoring approximately 500 feet of conductor. Thus one ten foot containerprovides sufficient cable to span about 16 sections of 30 foot drillpipe. FIG. 1 illustrates the conductor string 22 as having threecontainers 26. The lower two containers, as illustrated, have dispensedtheir stored cable for lengthening the conductor 22 at the point ofoperations illustrated in FIG. 1.

It should be realized, of course, that the container 26 may be longerthan that illustrated in the drawings but for convenience it ispreferred that relatively short containers be used. If high strengthcable, such as armored cable, is used as the conductor string 22, thecontainers 26, conductor 22 and connectors can be constructed in aself-supporting fashion. However, if the conductor 22 does not include areinforcing steel sheath or tension wire, the system may includereinforcing spiders for supporting each container and its conductorsection at spaced intervals within the drill string. One spider 30 isillustrated in FIGS. 1 and 3 as being mounted at a joint in the drillstring 12 and serving to support the bottom container 26 and itsassociated cable.

As illustrated in FIG. 2, the container 26 is constructed in two tubularsections 27 and 28 adapted to be joined in end-to-end relation by meansof a suitable fastener such as screws. Upper section 27 contains a firstportion of coiled cable illustrated as 31 and lower section 28 containsa second portion of coiled cable 32. Coiled cable portions 31 and 32 arewound in opposite hands; that is, portion 31 is arranged in right-handspiral and portion 32 in a left-hand spiral. The inner ends of coiledportions 31 and 32 are each secured to the inner wall of theirrespective sections 27 and 28 by bolt and clamp assemblies 33 and 34.The purpose of the clamp assemblies is merely to retain the cable 22 securely to the container 26 after the coiled portions have been paid out.The portions 31 and 32 arranged in opposite hands may be one continuouscable, but in order to facilitate loading the container, it is preferredthat they be separate cable sections joined by connectors 35a and 35b.The coiled portions 31 and 32 being wound in opposite hands, upon beingdispensed at about the same rate or alternately from their respectivecompartments, will prevent twists from forming in the conductor string22.

Means are provided for controlling the dispensing of the coiled portions31 and 32 of the cable from the container 26. A first cable clutchassembly 36 at the lower end of the container 26 is adapted to grip astraight portion 38 of the cable to retain the coiled portion 32 withinlower section 28. Upon being actuated, assembly 36 permits stored cableto be fed out or dispensed from the lower end of container 26. As itunwinds, the cable passes through the clutch assembly 36 and therebylengthens the conductor string 22.

A second cable clutch assembly 37, positioned in the upper end ofcontainer 26 retains coiled cable within section 27. Upon being actuatedto a release position, assembly 37 permits cable to unwind and feed outthe upper end of container 26. Thus, it is seen that the telemetryconductor is lengthened by cable being unwound from both coiled portions31 and 32 and being fed out opposite ends of container 26. As notedpreviously, the portions 31 and 32, being wound in opposite hands,prevent the cable from twisting as individual coils are unwound at thesame time or alternately.

As described in more detail below, the upper clutch assembly 37 ismovable to its released position in response to actuation of the lowerclutch assembly 36. In this embodiment, the lower clutch assembly isactuably responsive to tension in conductor 22. By pulling the conductor22 upwardly at the surface, clutch assembly 36 releases which in turncauses the upper clutch assembly 37 to release.

As best seen in FIGS. 2 and 5, the lower clutch assembly 36 comprisesgripping rollers 40 and 41 arranged within the lower end of container 26such that the nip of the rollers engages straight portion 38 of thecable. Roller 40 serves as the main clutch and is mounted on bell crank42. Roller 41 serves as a backup for roller 40 and is mounted on arm 43.Bell crank 42 and arm 43 are pivotally mounted to support member 44which also supports guide roller 46.

A downwardly extending arm of the bell crank supports, in free-wheelingrelationship, roller 40 while the other arm extends outwardly throughopening 47 formed in the wall of container 26 and has an outer exposedend 50. The exposed end 50 is connected to rod 48 which interconnectsthe lower and upper clutch assemblies 36 and 37.

The bell crank 42 is urged inwardly forcing roller 40 to its normalcable engaging position by spring 49. Spring 49 is maintained inposition by retainers 51 and 52 which are fastened respectively to theinner wall of container 26 and bell crank 42. Arm 43 supports roller 41in free-wheeling relationship and is provided with stop 53 whichdetermines the backup position of roller 41. Spring 45 maintains rollers40 and 41 close together thereby maintaining the cable section properlyat the nip thereof. Guide rollers 56 and 57 mounted on support member 58are provided below the clutch assembly 36.

A brake assembly which forms part of the lower clutch assembly 36 isprovided immediately below the coiled cable 32 in section 28 to preventthe coils from unwinding. This assembly comprises a back-up roller 61eccentrically mounted on support member 62 which in turn is secured tothe container 26. A spring loaded, cable engaging member 63 is urgedtoward the eccentric roller 61 and is also supported by member 62. Thecable from coiled portion 32 thus passes downwardly between member 63and eccentric roller 61, around guide 46, through the nip of rollers 40and 41, between guide rollers 56, 57 and downwardly out the lower end ofcontainer 26. The lower terminal end of the cable is provided with aconnector 64 which is adapted to mate with a connector provided in theconductor string 22.

As shown in FIGS. 2 and 4, the upper clutch assembly 37 comprises acable gripping member 66 pivotally mounted to the upper section 27 as at67. Member 66 extends through opening 70 of section 27 and has an outerend disposed externally of container 26. Member 66 is adapted to grip anupper straight portion 69 of cable above coils 31 and is adapted tocooperate with back-up member 68 which is secured to the interior ofsection 27. As illustrated, members 66 and 68 are each provided with agrooved end for gripping cable portion 69. Cable unwound from coiledportion 31 passes through the nip of guide rollers 71 and 72, throughthe brake assembly 37, through an upper guide 73 which is secured tomember 68. The upper end of cable portion 69 terminates in connector 76which is adapted to mate with a connector of an adjacent cable section.

As mentioned previously, the upper clutch assembly 37 is actuated by thelower clutch assembly 36 through rod 48. Thus, tension in the conductorstring above the container 26 caused by the weight of the cable andcontainer or by pulling forces will not release coiled cable fromsection 27. Rod 48 is secured to the outer exposed ends 50 and 75 ofmembers 42 and 66 and in effect forms a linkage between the two clutchassemblies. Rod guides 79 spaced along the exterior of container 26maintains the rod in proper position.

In this embodiment the actuation of the lower clutch assembly 36 is bycable tension. In the relaxed position of the conductor string 22, thelower clutch assembly 36 is in the position generally as shown in FIG.2. In the relaxed position the spring 49 forces roller 40 into grippingengagement with cable portion 38 forcing the cable and back-up assemblyto the right stop position as viewed in FIG. 2. This prevents the cablefrom being pulled from the lower coiled section of the container 26.With roller 40 positioned in its normal gripping position, the brakemember 66 of the upper clutch assembly 37 will also occupy the brakingposition through the linkage comprising bell crank 42 and rod 48. Spring49 thus not only forces roller 40 into engagement with the cable betweenthe nip of rollers 40 and 41 but also forces member 66 into forcefulengagement with conductor portion 69.

An upward pulling force on conductor 22 imparts tension on the cablestring which tends to straighten cable portion 38 between guide rollers56, 57, and guide roller 46. This forces rollers 40 and 41 to thereleased position. Movement of roller 40 also moves clutch member 66away from cable portion 69 releasing the upper clutch assembly.Releasing of the upper and lower clutch assemblies 36 and 37, permitscable to be dispensed from opposite ends of the container 26. For eachloop of left-hand and right-hand coils dispensed, the container revolvesone revolution thereby preventing twists from forming in the cable. Thecable is dispensed by coiled portions being unwound and being fedthrough their respective clutch assemblies. As the cable is dispensedfrom opposite ends, for every left-handed wound coil a right-handedwound coil is released. Because of the eccentric roller 61, cable isdispensed interrnittenly from the lower end. When the lobe of theeccentric roller 61 engages the cable portion 38, the braking forcesincrease so that the rate of cable being dispensed is reduced. However,once the lobe is forced past the engagement position on the cable, thecable passes through the brake with less resistance thereby increasingthe rate at which it can be dispensed. The intermittent action of thebrake on cable 38 causes the left-hand and right-hand coils to beunwound and dispensed from the container alternatively.

There are a number of commercially available cables that aresufficiently flexible to permit such cable to be coiled in the mannerillustrated in FIG. 2. A particularly suitable cable is a singleconductor 12 AWG neoprene jacket conductor sold by Vector Cable Companyas 8-5025.

In order to facilitate the insertion of the coil conductor within thecontainer 26, it is preferred that the container 26 be constructed intwo sections as described previously. The conductor may be installedwithin each tube section 27 and 28 by winding conductor on a suitablemandrel. The mandrel with the conductor wound thereon is inserted into atube section as for example through the lower end of section 27. Anupper portion of the conductor provided with connector 76 is threadedthrough the guide rollers 71 and 72, the clutch assembly 37, the guide73, and finally out the upper end of section 27. A relatively long leadmay be provided at this end. With the conductor properly positioned insection 27, the mandrel is turned in the opposite direction of the coilsto release the grip of the coiled conductor, permitting the mandrel tobe removed from the coils and section 27. The lower end of the coiledcable 31 is clamped to the wall of section 27 leaving connector 35aexposed. The same procedure is used in mounting cable portion 32 withinlower section 28 except the coils in this section are wound in oppositehand relative to the coils in section 27. The lower lead extending fromcoiled portion 32 is threaded through the lower brake and clutchassemblies and may be provided with a relatively long lead extendingbelow the lower end of section 28. As mentioned previously, the lowerend of the cable terminates in connector 64. The upper end of the cablewithin tube section 28 is clamped to the interior wall thereof and theupper connector 35b is mated with the lower connector 35a of cableportion 32. The two tubular sections 27 and 28 are then fastenedtogether and the rod 48 connected to the clutch assemblies 36 and 37.

It should be noted that each cable container is constructed such thatthere will be very little resistance to the flow of fluids therethrough.During the drilling operations, drilling fluid will be pumped down thedrill pipe and will pass around and through the containers 26.

In describing operation of the present invention, it will be assumedthat the borehole 17 has been drilled to a certain depth usingconventional techniques and at this depth it is desired to commencedrilling-whilelogging operations. The drill string 12 and bit 13attached thereto is lowered into the borhole 17 in the usual manner. Theinstrument 21 is lowered on cable 22 and located at the proper depthwithin the drill string 12. The upper end of the conductor 22 is provided with a cable clamp and connector 77. The clamp and connector 77may be located in a spider 78 similar to spider 30 shown in FIG. 3 forsupporting the upper end of the cable on the drill string. Since thisinitial section of cable may extend several thousand feet, it ispreferably constructed of armored cable such as a single conductor 3/16-inch armored cable manufactured by the Vector Cable Company and soldas Type I-l8P.

With the conductor 22 properly located in the drill string 12, a pipesection 81 provided with a cable container 26 may be added into thesystem. This may be achieved by the following procedure described withreference to FIGS. 6, 7 and 8.

Pipe section 81 with the cable container 26 therein is elevated by therig hoisting equipment. The lower connector 64 is mated with connector77 and pipe section 81 is then screwed into the top section of the drillstring 12. The drill string and cable therein is lowered the length ofpipe section 81 and again suspended in the rotary table 16 (see FIG. 7).The kelly 11 is then connected to the next pipe section 84 placed in themouse hole 82 by threading the tail 24 of the kelly conductor into thepipe section 84 and screwing the kelly into the box end of pipe section84.

This assembly is then elevated above the drill string 12 and the kellycable is mated with connector 76.

The support plate 83 is then removed and the pipe section 84 is screwedinto the box end of pipe section 81. It should be noted that because ofthe excess length of the conductor and the kelly, there will be someslack in the conductor within pipe joint 81. However, this slack will beremoved by the addition of the next pipe joint to the drill string 12.

With the drill string 12 and conductor 22 lengthened, drilling mayproceed for another length of pipe permitting the monitoring of drillingconditions as desired. The individual sections of drill pipe can beadded in the same manner that pipe section 84 was added for eachincremental advance of the borehole 17. During the addition of secondand subsequent pipe sections, surplus cable is pulled from the coiledportions stored in container 26 permitting the lengthening of theconductor string 22 as the drill pipe 12 is lengthened. Each container26 will be provided with sufficient amounts of surplus cable in thecoiled configuration to accommodate several pipe joints. Whenthe-surplus cable is used up, a second container may be inserted intothe conductor string 22. If the cable used in the containers does nothave sufficient strength to support large loads, a spider may beprovided at the upper end of the conductor. This spider may be insertedimmediately prior to the addition of the next container and conductorsection. The spider may be of the same construction as that illustratedin FIG. 3.

Drilling operations may proceed as described previously using aplurality of the containers 26 in the conductor string 22. I

When it becomes necessary to interrupt drilling operations as forexample to change bit 13, the conductor 22 which by this time mayinclude several containers 26, may be removed by disconnecting the kelly11 and kelly conductor 24 in the manner described previously. The cablesections and associated container may be individually retrieved. Eachcable section is thus withdrawn from the drill string permitting theremoval of the same length of drill pipe before the next cable sectionis withdrawn.

Although the present invention has been described with reference tospecific types of equipment and cable, it should be realized thatnumerous modifications may be made without departing from the spirit ofthe invention. For example, the cable Within each container 26 may beprovided with internal tension members which increase the tensilestrength of the material. in this type of construction, the spiders atthe upper end of each cable section may not be required.

It should also be mentioned that the present invention may be used withdrilling equipment other than that described herein. For example, it maybe used in connection with turbodrills in positive displacementhydraulic motors. These devices normally include motor or turbinemounted on the lower end of the drill string and adapted to connect tothe drive or bit. The motor or turbine powered by the drilling fluiddrives the drill bit while the drill string remains stationary. Whenthis type of subsurface drilling equipment is used in directionaldrilling operations, the present invention provides a highly usefulmeans for transmitting directional data to the surface.

I claim:

1. Apparatus for use in an electric system employed in a pipe string toconduct electric signal between a subsurface location and a surfacelocation, which comprises a container adapted to be inserted in saidpipe string; an insulated electric conductor mounted in said containerand having a first portion wound in left-hand coils and a second portionwound in right-hand coils, said conductor being adapted for connectioninto the electric system; first conductor gripping means for dispensingconductor from the lower end of said container; and second conductorgripping means for dispensing conductor from the upper end of saidcontainer, said first and second conductor gripping means beinginterconnected so that conductor is dispensed from opposite ends of saidcontainer at about the same rate.

2. Apparatus as defined in claim 1 wherein said first conductor grippingmeans includes a member urged into engagement with said conductor at apoint below the coiled portions and wherein said second gripping meansincludes a member urged into engagement with said conductor at a pointabove the coiled portions, a linkage interconnecting said memberswhereby actuation of one member to its released position moves the othermember to its released position.

3. Apparatus as defined in claim 2 wherein said member of said firstgripping means is moved to the released position by tension in saidconductor.

4. Apparatus as defined in claim 1 wherein one of said conductorgripping means is operatively responsive to tension in the conductordispensed from said container.

5. Apparatus for maintaining electric circuit from a subsurface locationto the surface which comprises: a container capable of being loweredinto the pipe string, an electric conductor section having two coiledportions wound in opposite hands; one of said coiled por tions beingmounted in an upper section of said container and the other of saidcoiled portions being mounted in a lower section of said container;means for electrically connecting the upper coiled portion to a terminalabove said container; means for connecting the lower coiled portion to aterminal below said container; a lower conductor brake normallypositioned to engage said conductor at a point below said coiledportions and being movable to release said conductor; and an upperconductor brake normally positioned to engage said conductor at a pointabove said coiled portions and being movable to release said conductor,said upper conductor brake being movable to the release position inresponse to movement of said lower conductor brake.

6. Apparatus as defined in claim 5 and further comprising means forsupporting said container on said pipe string.

7. Apparatus for insertion into a pipe string which comprises: acontainer having upper and lower coiled portions mounted therein, saidcoiled portions being wound in opposite hands and having upper and lowermeans for dispensing portions of conductor from opposite ends of saidcontainer, said upper and lower dispensing means being interconnectedsuch that conduc tor is dispensed from opposite ends of said containerat about the same rate.

8. Apparatus as defined in claim 5 wherein said container is free torevolve within said pipe string such that as coiled conductor isdispensed from its opposite ends, said container revolves preventingtwists from forming in said conductor.

1. Apparatus for use in an electric system employed in a pipe string toconduct electric signal between a subsurface location and a surfacelocation, which comprises a container adapted to be inserted in saidpipe string; an insulated electric conductor mounted in said containerand having a first portion wound in left-hand coils and a second portionwound in right-hand coils, said conductor being adapted for connectioninto the electric system; first conductor gripping means for dispensingconductor from the lower end of said container; and second conductorgripping means for dispensing conductor from the upper end of saidcontainer, said first and second conductor gripping means beinginterconnected so that conductor is dispensed from opposite ends of saidcontainer at about the same rate.
 2. Apparatus as defined in claim 1wherein said first conductor gripping means includes a member urged intoengagement with said conductor at a point below the coiled portions andwherein said second gripping means includes a member urged intoengagement with said conductor at a point above the coiled portions, alinkage interconnecting said members whereby actuation of one member toits released position moves the other member to its released position.3. Apparatus as defined in claim 2 wherein said member of said firstgripping means is moved to the released position by tension in saidconductor.
 4. Apparatus as defined in claim 1 wherein one of saidconductor gripping means is operatively responsive to tension in theconductor dispensed from said container.
 5. Apparatus for maintainingelectric circuit from a subsurface location to the surface whichcomprises: a container capable of being lowered into the pipe string, anelectric conductor section having two coiled portions wound in oppositehands; one of said coiled portions being mounted in an upper section ofsaid container and the other of said coiled portions being mounted in alower section of said container; means for electrically connecting theupper coiled portion to a terminal above said container; means forconnecting the lower coiled portion to a terminal below said container;a lower conductor brake normally positioned to engage said conductor ata point below said coiled portions and being movable to release saidconductor; and an upper conductor brake normally positioned to engagesaid conductor at a point above said coiled portions and being movableto release said conductor, said upper conductor brake being movable tothe release position in response to movement of said lower conductorbrake.
 6. Apparatus as defined in claim 5 and further comprising meansfor supporting said container on said pipe string.
 7. Apparatus forinsertion into a pipe string which comprises: a container having upperand lower coiled portions mounted therein, said coiled portions beingwound in opposite hands and having upper and lower means for dispensingportions of conductor from opposite ends of said container, said upperand lower dispensing means being interconnected such that conductor isdispensed from opposite ends of said container at about the same rate.8. Apparatus as defined in claim 5 wherein said container is free torevolve within said pipe string such that as coiled conductor isdispensed from its opposite ends, said container revolves preventingtwists from forming in said conductor.